1. Field of the Invention
The present invention relates to an apparatus and a method for realizing gray levels, and more particularly to an apparatus and a method, in which gray levels are realized in such a manner that a pixel is supplied with a constant current instead of a voltage and charging duration (required for inputting data until a gate is turned on/off) is time-divided by the number of gray levels to be realized.
2. Description of the Prior Art
As generally known in the art, a liquid crystal display (LCD) device has a plurality of pixels arranged in a matrix structure between a plurality of data lines and a plurality of scan lines, and an anode and a cathode of each pixel are linked with the data line and the scan line, respectively, so that one display panel is formed. Such an LCD emits light to a pixel when a voltage difference between the data line and the scan line exceeds a threshold voltage of the pixel and varies the brightness of the pixel according to time during which a current flows in the pixel, so that a variety of gray levels can be realized.
FIG. 1 is a block diagram illustrating a structure of the conventional apparatus for realizing gray levels.
The conventional apparatus includes a shift register 10, a data register 11, a data latch 12, a level shifter 13, a reference voltage generator 14, a D/A converter 15, and an output butter 16.
The shift register 10 supplies edge sampling clocks to the data register 11, and the data register 11 loads RGB data supplied from a timing controller (not shown) according to the edge sampling clocks provided from the shift register 10. Thereafter, the RGB data are stored as all display data through one horizontal line and then move into the data latch 12.
The reference voltage generator 14 receives a gamma voltage inputted from an external device so as to generate gray levels of 256 (8 bits) or gray levels of 64 (6 bits) through an internal R-string circuit.
The DA converter 15 receives the display data outputted from the data latch and generates an output voltage corresponding to the input display data based on a reference voltage of each gray level provided from the reference voltage generator 14.
The output buffer 16 including an operation amplifier for driving an LCD panel maintains a predetermined voltage for scan duration of one horizontal line through which output signals of the output buffer 16 are input once. Charging time for all input gray levels is equal to the scan duration of one horizontal line, and each different voltage is required in order to output each different gray level. However, the conventional apparatus for realizing gray levels has a limitation in the realization of various gray levels because the range of input gamma voltages is small. In other words, a gamma voltage inputted to the conventional apparatus for realizing gray levels has a voltage level of 5 mV. Therefore, the conventional apparatus for realizing gray levels cannot realize a variety of gray levels due to a small level of a gamma voltage when the apparatus realizes gray levels of 1024 (10 bits) or more.